I've always put them on the rear frame rail. the inboard side.

how far from to fuel cell? The only spot i can mount on the inside of the rear rail is about 3 feet from the pickup.

I use a bracket to hang down from the frame rail and get the pump mounted to that preferably to the rear corner of the fuel cell.

I put my street Magnafuel 275 pump in the right rear corner of the rear sub frame on my old pump gas Duster using the stock tank with a welded in center sump with a #12 AN fitting welded into the sump facing the rear bumper
The bottom of the pump was even with the bottom of the tank but higher than the bottom of the added sump

OK new question

MSD says to pickup power and ground directly from the battery- I have always done this, but is it really necessary?

I have done both, seen both. If you are having trouble I personally have never seen going directly to the battery fixing it. It was always a faulty component. So necessary ....imo no. Just make sure you use sound wiring techniques.Good chassis/engine ground, use the the heavy wire coming from the battery for your pick-up point. If you want to get technical, check your voltage drop/ resistance to ground at different points.

Yea, I am going to try it but just going to the lug on the starter for my pickup and a a solid ground elsewhere. Hope it works!

How do you install the rear quarter glass in a tubbed car. I have it in the spot where i want it to live, obviously due to tub size they will never move, but what do you do to mount them solid?

anybody know how to pin the glass in?

Everything I have seen still had the track and regulators. But I would think you could use the original Hole in the glass and fab a bracket over and out to the inner structure and mount there.

Some Challengers came with no roll up rear side windows, I'm not sure if Plymouth had them in the E body Cuda or not
Maybe a diagram of the stock Challengers would help you

. Prop the window in there , hold it in with some duct or 2" masking tape. Look at the bottom of the window, should have some hole to bolt it to the regulator. Get some flat 1" or 1 1/2" alum from a hardware or Home Depot. Bolt it to the window and somewhere to hol the window in place. Hope that helps

awesome, thank you guys!

can't help you on the side window , but I have always mounted the fuel pump as close to the sump as I could.
Most electric pumps prefer to push fuel as opposed to drawing it.